Combines are known in the art. They are available in various designs and models to perform the basic functions of harvesting, threshing, and cleaning of grain. As used herein, the term "grain" is meant to include corn, wheat, rye, oats, barley, flax seed, sorghum, soy beans, mixed grain, and any other food grains, feed grains, and oil seeds.
A typical combine includes a crop harvesting apparatus which reaps planted grain stalks. An infeed mechanism arranged at the forward end of the combine operates in combination with the harvesting apparatus and feeds the grain stalks to a separating apparatus. The separating apparatus threshes and separates the grain from the material other than grain.
While the separating apparatus acts to separate a substantial portion of the crop or grain from the material other than grain, some chaff and/or straw remains intermixed with the grain and a further cleaning or separating action is normally required. Further separation is normally achieved in a cleaning section of the combine.
The cleaning section of a conventional combine is located to receive grain and other material expelled from the separating apparatus. A typical cleaning section includes two reciprocally mounted sieves and a fan which produces a flow of air directed through the sieves. Reciprocation of the sieves facilitates arrangement of the grain and other materials into a crop layer or mat on top of the sieves. Each sieve preferably includes a series of adjacent louvers. A series of transversely elongated openings or passages is defined between the adjacent louvers to grade the material by size such that smaller kernels are allowed to fall through the openings but causing larger pieces of material to be moved rearward and off the sieves. The material moved off the sieves is returned to the separating apparatus for rethreshing.
Separation of the crop material is facilitated by the air from the fan flowing upwardly through the passages between the louvered sieves. The upwardly directed air creates a force which urges residue material including straw, chaff and the like to float on top of the sieve and into an airborne state such that it may be directed toward and expelled from a discharge end of the combine. The heavier seeds or clean grain tend to move to the sieve and fall through the openings or passages into a clean grain collector.
A substantial amount of chaff, straw and the like passes to the cleaning section of the combine from the separating apparatus. This forms a conglomerate mass of clean grain and chaff which is difficult to clean. As will be appreciated, the chaff acts to clog the sieve and, thereby, retard and sometimes inhibit clean grain from passing therethrough. As is evident from the prior art, considerable effort regarding fan design has been done over the years to produce an efficient flow of air which is necessary to provide a proper cleaning action for the threshed crop material.
To enhance versatility of the combine such that it can be used to harvest more than one type of grain, the louvers on the cleaning sieves are angularly adjustable relative to each other. The angular adjustability of the louvers allows the size of the openings or passages between adjacent louvers to be changed to control the size of the material that is allowed to fall through the passages or openings and thereby achieve the desired degree of material grading.
Successful operation of the prior art devices relies in large part on the proper opening between the louvers. If these openings are too small for the particular material being harvested, there is naturally a significant increase in the thickness of the layer of crop material on the sieves. Thus, the effectiveness of the fan is diminished. Moreover, a large portion of the clean grain is not allowed to pass through the sieve. Instead, the clean grain is moved off the rear of the sieve and repeated to the separating apparatus. The increase in material being repeated to the separating apparatus has an adverse effect on the productivity of the combine and enhances the opportunity for grain cracking. When the passages or openings between adjacent louvers are too small, harvester productivity is adversely effected because the ground speed of the harvester is necessarily reduced to inhibit excessive grain loss onto the ground.
On the other hand, if the openings or passages between the louvered sieves are too large, material other than grain passes into the collection chamber contaminating the clean grain sample. Sufficient contamination of the grain contained in the clean grain sample will cause a severe reduction in the price received for the grain when marketed. Accordingly, the openings between the louvers must be carefully regulated and controlled to inhibit the amount of material other than grain passing into the clean grain sample. Alternatively, the material other than grain can be mechanically removed or separated from the clean grain by a secondary operation away from the combine. As will be appreciated, such secondary operations are laborious, time consuming and, therefore, costly to the farmer.
The problem of separating material other than grain from clean grain is exacerbated in small grain cereal crop, especially wheat. Under certain climatic conditions, there is a tendency for the husk surrounding the grain to be tightly held to the kernel. This causes a condition known as "white caps" in the grain sample. These are grains that did not get thoroughly threshed in the separating apparatus, but did manage to fall into the clean grain portion of the harvester. Since the white caps are only slightly larger than the clean grain kernel, it is very hard to set the opening between the louvers to a dimension that will allow clean grain passage, but reject the white caps for return to rethreshing. This adjustment also necessitates microadjustments of the sieve opening that amount to changes of little more than a paper thickness. Of course, this fine an adjustment with the mechanism provided is very difficult and most frustrating.
The foregoing illustrates numerous problems and limitations of the known prior art mechanisms. Thus, it is apparent that it would be advantageous to provide cleaning sieves which facilitate air and grain flow therethrough while discerning between clean grain and material other than clean grain.